Many early rotating electrostatic motors used a central bearing with various arrangements of electrostatic stators around the motors to effect rotation. Unfortunately, these motors tended to have problems with friction at the central bearing and have had lifetime issues related to wear of the bearing. The motors typically acted as stepper motors where the rotor rotates with an incremental motion as the stator elements are attracted. Thus it was difficult to precisely adjust a plate to a particular angle with such motors.
Other angular motors have been described which use flexural elements to support a rotating element. Comb drive fingers are arranged in concentric arcs around a central flexural pivot, so that small angular motion is provided around the pivot. See, for example, D. A. Horsley, et al., "Angular Micropositioner for Disk Drives", Proceedings of the Tenth International Workshop on Micro Electro Mechanical Systems, 1997, pp 454-458; L.-S. Fan, et al., "Batch-Fabricated Area-Efficient Milli-Actuators", Proceedings 1994 Solid State Sensor and Actuator Workshop, Hilton Head, pp 38-42; T. Juneau, et al., "Dual Axis Operation of a Micromachined Rate Gyroscope", Proceedings 1997 International Conference on Solid State Sensors and Actuators, V.2, pp 883-890; E. H. Klaassen, et al., "Silicon Fusion Bonding and Deep Reactive Ion Etching; A New Technology for Microstructures", The 8th International Conference on Solid-State Sensors and Actuators, and Eurosensors IX, Stockholm, Sweden, Jun. 25-29, 1995, pp 556-559; W. C. Tang, et al., "Laterally Driven Polysilicon Resonant Microstructures", Sensors Actuators 20, 1989, pp 25-31 (IEEE reprint pp. 53-59) and U.S. Pat. No. 5,025,346 to Tang et al. Unfortunately, all of these devices provide a limited angular range of motion.
Other electrostatic microactuators with improved angular range of motion have been provided for rotating devices such as optical components. See, for example, International Publication No. WO 00/36740 to Jerman et al. It has been found, however, that such components may require additional positional adjustments during use due to initial placement errors or subsequent misalignments resulting from temperature changes or other environmental factors.
In general, it is an object of the present invention to provide a rotary electrostatic microactuator having a movable member that can be adjusted during use in a direction other than its primary direction of angular motion.
Another object of the invention is to provide a rotary electrostatic microactuator of the above character in which the movable member can be tilted about an axis extending substantially parallel to the substrate of the microactuator.
Another object of the invention is to provide a rotary electrostatic microactuator of the above character in which the movable member can be tilted relative to the movable comb drives of the microactuator.